Visible Light Emission Research Articles

Visible light emissions during flash sintering of 3YSZ are thermal radiation

Flash sintering enables the densification of ceramics at low furnace temperatures in a few seconds by the application of an electric field to the specimen. One of the earliest mechanisms proposed to explain the rapid densification involves the generation of Frenkel defects. Light emission during flash sintering is often interpreted as electroluminescence from electron-hole pair recombination, in support of this mechanism. In this work, experimental investigation of the emissions during flash sintering of the most widely studied ceramic, 3YSZ, shows that the visible spectrum can be explained completely in terms of black body (thermal) radiation resulting from the Joule heating of the specimen rather than electroluminescence. Apparent peaks in the spectrum are experimental artefacts associated with the equipment. There is no evidence in the visible emission spectrum during flash sintering of 3YSZ for electron-hole pair recombination associated with Frenkel pair formation or for any mechanism other than Joule heating.

Investigation on the material properties of ZnO nanorods deposited on Ga‐doped ZnO seeded glass substrate: Effects of CBD precursor concentration

Optimized Ga‐doped ZnO (GZO) seed layer was coated onto a glass substrate where ZnO nanorods (ZNRs) were grown via a facile chemical bath deposition (CBD) technique. The concentrations ([Zn (NO3)2]/[C6H12N4]) ratio was maintained at 1, at 90°C for 90 min. Lower thermodynamic barrier was used. This was achieved by growing a GZO NPs seed layer that provided nucleation sites which in turn enhanced the optical properties and the aspect ratios hence ensuring uniform distribution of ZNRs. Investigations of CBD growth concentrations (0.005, 0.03, 0.05, 0.07, and 0.1 M) effects on the material properties of ZNRs were carried out. The as‐prepared ZNRs displayed crystalline wurtzite structures. The observed structure had c‐axis preference in most of the obtained samples. An increase in size of the crystallites and 002 peak intensity was observed as the growth concentration increased. The SEM micrographs and AFM images showed a direct relation between the length, particle size of the ZNRs, and the precursor concentration. Similarly, the PL spectra showed the excitonic peak intensity increased to a maximum at a precursor concentration of 0.05 M and decayed as the concentration levels increased. Enhancement of the UV and visible light emissions intensity ratios of the ZNRs prepared at lower concentrations was also observed. This is an indication of high optical quality. A higher %T at lower growth concentration and variation of the band gap energy values (3.10–2.30 eV) as the growth concentration is increased were observed from the UV‐VIS analysis. The as‐prepared ZNRs samples deposited on GZO transparent conducting film were highly luminescent composing of well‐aligned ZNRs and perfect crystallization obtained at the 0.05 equimolar precursor concentration of [Zn (NO3)2]/[C6H12N4] solution. The as‐grown ZNRs with the observed material properties can be applied in dye‐sensitized solar cells production, serving as a photoanode.

Photocatalytic activity of Eu-doped ZnO prepared by supercritical antisolvent precipitation route: When defects become virtues

• Eu-doped ZnO at different Eu content were synthetized by SAS process. • Eu-doped ZnO provides novel defect sites and higher hydrophilicity. • Photocatalytic activity was assessed under UV light. • The optimal Eu content for crystal violet and ferulic acid degradation was 1 mol%. • A lower hydrophilicity induced a higher vanillin selectivity. The aim of this work is to determine the structural and optical properties of Eu-doped ZnO powders prepared by supercritical antisolvent precipitation route (SAS) and to correlate the physico-chemical features with the photocatalytic activity under UV light. Raman and EPR spectroscopy highlight the introduction of novel defects (mainly singly and doubly ionized oxygen vacancies, and oxygen interstitials) on the Eu-doped ZnO samples, which confer higher hydrophilicity to the doped samples with respect to bare ZnO, as evidenced by FT-IR analysis. Additionally, photoluminescence spectra show that the presence of Eu 3+ totally quenches the visible light emission typical of bare ZnO, which mainly results from the recombination of photogenerated holes at defective sites. The prepared samples were tested both for the photocatalytic degradation of crystal violet dye (CV) and for the partial oxidation of ferulic acid under UV irradiation. The photocatalytic activity results evidence of a higher ability of Eu-doped photocatalysts to degrade CV and ferulic acid, while higher selectivity values towards vanillin are obtained in the presence of bare ZnO. The higher activity of Eu-doped ZnO photocatalysts is linked to the stabilization of photogenerated holes and to their higher hydrophilicity, both brought by the generation of defective sites induced by the presence of Eu 3+ ions within the ZnO lattice.

Investigation of Electronic and Optical Properties of Al/Ag and Al/N Co-Implanted ZnO Thin Films

Either metal/metal or metal/non-metal co-doping is one of the most effective methods to modulate the visible emission of ZnO. In this paper, ZnO, aluminum-doped ZnO (Al-ZnO), aluminum and silver co-doped ZnO (Al/Ag-ZnO), and aluminum and nitrogen co-doped ZnO (Al/N-ZnO) are deposited. Combining the substitution of zinc ions using Al and/or Ag doping and the substitution of oxygen ions using N doping is expected to introduce more interstitial zinc and oxygen vacancy defects related to visible light emission in ZnO films. The results indicate that the PL spectrum of ZnO shows a violet emission peak at 406 nm and other weak visible emission peaks. After Al doping, we observe a strong blue emission at 421 nm, and its intensity is further enhanced and attains the maximum for Al/N-ZnO. However, for Al/Ag-ZnO, the blue emission shifts toward a longer wavelength, and the intensity of the blue emission conversely decreases. Then, the band structures, the density of states (DOS), the partial density of states (PDOS), and the optical constant of doped ZnO are calculated using density functional theory (DFT). Based on the experimental and theoretical results, the enhancement mechanism of visible light is discussed.

Effect of Yb[formula omitted] concentration on Er[formula omitted] doped CaF[formula omitted] single crystal for temperature sensor applications

Yb–Er co-doped CaF2 crystals with different Yb3+ ions concentrations are successfully grown by the temperature gradient technique (TGT) method. Up-conversion (UC) luminescence characteristics and optical temperature sensing behavior of all samples are thoroughly investigated in this work. Under the excitation of a 980 nm laser-diode, the up-conversion luminescence intensity firstly increases and then decreases. By adjusting the content of Yb3+ ions, multi-color visible light emissions of red, yellow and green could be easily obtained. The fluorescence intensity ratio from two thermally coupled 2H11/2 and 4S3/2 levels technology is used to evaluate the temperature sensing performance of Yb–Er co-doped CaF2 crystals. The concentration of Yb3+ ions shows a significant influence on the temperature sensing performance. The sensitivity reaches the maximum value of 2.24 × 10−3 K−1 at 548 K with a 5 at.% doping concentration of Yb3+ ions. The experiment also confirms that Yb–Er co-doped CaF2 crystal exhibit high stability as optical temperature sensors. In general, it is proved that Yb–Er​ co-doped CaF2 single crystals are a kind of promising materials used in the optical temperature sensor.

Aluminum–nitrogen co‐doping improves the blue emission of ZnO films: A combined theoretical–experimental study

AbstractThe investigation on visible emission of ZnO is necessary due its potential application in electrochemical communication, biosensor, and white light diodes, and so forth. Previous report indicates that the visible light of ZnO is related to the defect type and concentration. It can be regulated by various methods. However, quenching of light emission occurs if too many defects are introduced. In this work, combined with theoretical calculation about energy band structure, aluminum–nitrogen co‐doped ZnO is conducive to form p‐type semiconductor, but aluminum doped ZnO films tend to form a deep n‐type semiconductors. Therefore, in the experiment, aluminum–nitrogen co‐doped ZnO films are prepared using radio frequency magnetron sputtering. The substitution of oxygen using nitrogen impurity is expected to introduce more oxygen vacancies and interstitial zinc defects related to visible light emission. At the same time, annealing in vacuum is also a highly non‐equilibrium processes with low oxygen and high zinc contents. Results indicate that combined with aluminum–nitrogen co‐doping and an appropriate annealing temperature, the blue and blue‐green emission of ZnO films can be greatly improved.

Strain Effects in Wurtzite Boron Nitride: Elastic Constants, Internal Strain, and Deformation Potentials from Hybrid Functional Density Functional Theory

Boron‐containing III‐nitride heterostructures have recently attracted significant attention for improving the efficiency of visible and UV light emitters. However, the fundamental material properties of wurtzite (WZ) boron nitride (BN) are largely unexplored. Here, highly accurate first‐principles calculations are used to gain insight into internal strain, elastic constants, and electronic band structure deformation potentials. These parameters are key ingredients for simulating, and thus predicting, electronic and optical properties of boron‐containing III‐nitride‐based light emitters. The ab initio calculations show, for instance, that the quasi‐cubic approximation for deformation potentials is a poor approximation for WZ BN.

Delta InN-InGaN Quantum Wells With AlGaN Interlayers for Long Wavelength Emission

An active region design based on InGaN / delta-InN quantum well (QW) with AlGaN interlayer (IL) and GaN barriers (delta-structure) is investigated for potential high-efficiency visible light emitters. Numerical simulations demonstrate a large wavelength redshift with a simultaneous increase of the electron-hole wavefunction overlap for the delta-structure as compared to the conventional InGaN QW with AlGaN IL and GaN barriers. Proof of concept experimental growths via the metalorganic chemical vapor deposition demonstrate the effect of the delta-InN insertion into the conventional InGaN-based QW.

Mechanochemical synthesis of stable, quantum-confined CsPbBr3 perovskite nanocrystals with blue-green emission and high PLQY

Cesium lead halides are a family of bright, visible-light emitting materials with near-unity photoluminescence quantum yield (PLQY) in nanocrystals (NCs). The usual way to achieve visible light-emission tunability is by mixing halides, which often leads to phase separation and poor stability. While the NCs should also show size-dependent PL emission, reports on strong quantum confinement in these materials are scarce. Here, we report the synthesis of quantum-confined cesium lead bromide (CsPbBr3) NCs via a facile, environment-friendly, and scalable high-energy mechanochemical synthesis route. The PLQY measured is ∼85%, even after 90 days of synthesis, and the emission wavelength is shifted from green, 520 nm, to blue, 460 nm by quantum confinement in NCs of size 3–5 nm. Micro-PL optical spectroscopy and atomic force microscopy confirm the size tunability of PL on a single-dot scale. Our work demonstrates the potential of mechanochemical synthesis in the medium-scale production of bright luminescent quantum-confined NCs that could be extended to other materials as well.

Explorations on Growth of Blue-Green-Yellow-Red InGaN Quantum Dots by Plasma-Assisted Molecular Beam Epitaxy.

Self-assembled growth of blue-green-yellow-red InGaN quantum dots (QDs) on GaN templates using plasma-assisted molecular beam epitaxy were investigated. We concluded that growth conditions, including small N2 flow and high growth temperature are beneficial to the formation of InGaN QDs and improve the crystal quality. The lower In/Ga flux ratio and lower growth temperature are favorable for the formation of QDs of long emission wavelength. Moreover, the nitrogen modulation epitaxy method can extend the wavelength of QDs from green to red. As a result, visible light emissions from 460 nm to 622 nm have been achieved. Furthermore, a 505 nm green light-emitting diode (LED) based on InGaN/GaN MQDs was prepared. The LED has a low external quantum efficiency of 0.14% and shows an efficiency droop with increasing injection current. However, electroluminescence spectra exhibited a strong wavelength stability, with a negligible shift of less than 1.0 nm as injection current density increased from 8 A/cm2 to 160 A/cm2, owing to the screening of polarization-related electric field in QDs.

Effective regulation of upconversion luminescence in NaErF4 and NaErF4@SiO2 core-shell particles

Upconversion luminescence materials have gained extensive attentions owing to their unique luminescence characteristics of converting near-infrared excitation to visible light emission. However, how to improve the doping concentration of activator (usually <3 mol%) in traditional sensitizer-activator system is still a great challenge due to the luminescence quenching effect. In this work, NaErF4 crystals with diverse crystal phases and morphologies were prepared by simple hydrothermal method, constructing a 100% doping concentration system of activator (Er3+). With the increase of F− content, the phase of NaErF4 transfers from cubic to hexagonal, and the morphology changes from nanospheres to hexagonal microflakes, meanwhile, the upconversion luminescence intensity also increases gradually. In addition, in order to further inhibit the luminescence quenching effect of NaErF4 bare core, a series of NaErF4@SiO2 core-shell samples with different SiO2 shell thickness were successfully prepared. Compared with NaErF4 bare core, the morphology and structure of the NaErF4@SiO2 core-shell samples have no obvious change, but the UC luminescence intensity is significantly enhanced. Interestingly, the change of NaErF4 crystal phase and SiO2 shell thickness can both bring about multicolor luminescence. In addition, different from the traditional NaYF4:Yb, Er co-doping system, the as-prepared hydrophilic NaErF4 and NaErF4@SiO2 samples showed a greater red to green ratio (R/G > 1), which may expand their potential applications in biological imaging and sensing fields.

Tin sulfide-based nanocomposite: synthesis and study of structural, morphological and optical properties

A facile one-step chemical method has been developed for synthesize of SnS-based nanocomposites. Herein, we have prepared a series of SnS based nanocomposites such as SnS/CdO, CdO/SnS, SnS/PbO, PbO/SnS, SnS/PbS and PbS/SnS. The synthesized nanocomposites were characterized using X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared (FT-IR), UV-visible and Photoluminescence (PL) spectroscopy. The obtained results are discussed in details. Significant PL sifting observed for SnS based nanocomposites. The role of the various compounds added with SnS is mainly for tunning the optical emission of the SnS. The obtained visible light emission of the SnS-based nanocomposites can be used in the optoelectronic applications.

Theoretical insights into the central “acceptor” bridge function on the whole visible light and near-infrared emission in tetraphenylpyrazine-based luminogens

The whole visible light and near-infrared emission can be realizedviamodification of the central bridges in TPP-based luminogens.

Optical gain analysis of GaInP/AlGaInP nanoscale heterostructure for applications in visible light emission

In quantum well structures, charge carriers are confined in the well region and barrier region due to the discontinuity in the bandgap and larger built-in potential. Thus, for a smaller current, we can have a higher gain. This work reports the energy wavefunction and optical gain analysis of the GaAs-based quantum well structure made of GaInP/AlGaInP material layers. The structure is also examinedsubject to the effect of external pressure and temperature to study the tunability. The designed structure shows stability near the room temperature. The 6 × 6 Hamiltonian matrix is solved and the Luttinger-Kohn model with the conduction band is used for the calculation of band structure. In the quantum well structure, the thickness of the active layers is in our control. This is an important advantage for device fabrication. The material and the size of the layers are selected on the basis of their suitability to generate the radiation in the range of the red spectrum (620-–750 nm).The designed QW heterostructure is thus found to be suitable for photodynamic treatment (PDT) and dermatological treatments.

Visible Light Emissions During Flash Sintering of 3YSZ are Thermal Radiation

Visible Light Emissions During Flash Sintering of 3YSZ are Thermal Radiation

Visible Light Emissions During Flash Sintering of 3YSZ are Thermal Radiation

Visible Light Emissions During Flash Sintering of 3YSZ are Thermal Radiation

Monolithically Fabricated Waveguide for Efficient Guiding and Emission of Visible Light for IoT Applications

Monolithically Fabricated Waveguide for Efficient Guiding and Emission of Visible Light for IoT Applications

Fabrication of ultra-bright carbon nano-onions via a one-step microwave pyrolysis of fish scale waste in seconds

Carbon nano-onion is synthesized via microwave pyrolysis of fish scale waste in seconds. Simultaneous surface functionalization facilitates bright visible-light emission and excellent dispersibility, enabling the fabrication of flexible film and LED.

Synthesis and study on optical properties of CeO2-Mg(OH)2 and inverted Mg(OH)2-CeO2 nanocomposites

Well-crystalline CeO2-Mg(OH)2 and inverted Mg(OH)2-CeO2 nanocomposites were successfully synthesized by a facile ‘one-pot’ chemical precipitation method at low temperature. The crystal structure, morphology and optical properties of the CeO2- Mg(OH)2 and inverted Mg(OH)2-CeO2 nanocomposites were investigated using X-ray diffraction, TEM, FTIR, UV-vis absorption and PL spectrometer. The photoluminescence study revealed visible light emission for the nanocomposite. Interestingly, significant red shift observed for Mg(OH)2-CeO2 nanocomposites. The optical tuning nanocomposites can be used for the optoelectronic applications.

Effect of cation concentration and annealing temperature on structural, morphological, optical, and electrical properties of spin coated zinc-tin-oxide thin films

The current report focuses on the properties of Zinc–Tin-Oxide (ZTO) thin films coated on quartz substrates via spin coating technique. The two parameters considered during the thin film preparation and post deposition treatment include the cation concentration (Zn and Sn) in the precursor solutions and air annealing temperatures. Films were grown by using precursor solutions with different concentrations in the range 0.2–0.6 M and annealed at various temperatures between 600 and 900 °C. The X-ray diffraction studies revealed that the films annealed at 700 °C exhibit high crystallinity with a mixed phase of Zn2SnO4 and SnO2 for all the cation concentrations. FESEM images infer the growth of these films with closely packed porous structure uniformly covering the substrate. Raman spectra revealed the presence of characteristic vibrational modes of Zn2SnO4 at 378 and 669 cm−1 for higher cation concentration samples annealed at 700 °C. The optical studies revealed that the films exhibited high transmittance and the bandgap estimated was found in the range of 3.6–3.9 eV for all films. The visible light emissions due to defect centres located within the forbidden gap in ZTO films was evident through the photoluminescence studies. The electrical measurements of the annealed samples for different cationic concentrations yielded resistivity values in the range of 103 to 102 Ω-cm.